Well, a heap is just a bunch of memory (allocated
in contiguous extents) and you can practically allocate any size of chunk
of memory from it (with some restrictions). A regular heap has freelist and LRU
list mechanisms for managing space in it as well as memory
allocation/releasing routines which you can then call. Oracle uses its generic
heap manager code (KGH) for managing it's memory.
Once you allocate a
chunk from heap it's up to the allocator what he does with it. It can just use
it for some kind of static data, but can also create another heap in these
chunks it allocated, this heap may use different heap manager code for managing
its memory if needed (for example shared pool reserved area and large pool
behave a little differently, they don't have LRU list
mechanisms).
If you take any heapdump using alter session
set events 'immediate trace name heapdump level x' ; then top level heaps show
parent=00000000 in their descriptors. Note that this "top call heap" has
allocated chunks for heap with descriptor address 06B51DB0
(callheap) and also you see that "callheap" has a parent heap with
descriptor address 06B52790.
HEAP DUMP heap name="top call
heap" desc=06B52790
extent sz=0x213c
alt=92 het=32767 rec=0 flg=2 opc=2
parent=00000000
owner=00000000 nex=00000000 xsz=0xfffc
EXTENT 0 addr=071D0004
Chunk 71d000c sz= 112
perm
"perm "
alo=112
Chunk 71d007c sz=
65412 free
"
"
EXTENT 1 addr=07170004
Chunk 717000c
sz= 232
perm
"perm "
alo=232
Chunk 71700f4 sz=
60724 free
"
"
Chunk 717ee28 sz=
1352 freeable
"callheap " ds=06B51DB0
Chunk 717f370
sz= 1072 freeable
"callheap "
ds=06B51DB0
Chunk 717f7a0
sz= 1072 recreate
"callheap "
latch=00000000
ds 6b51db0
sz= 3496 ct=
3
[snipped....]
HEAP DUMP heap
name="callheap" desc=06B51DB0
extent sz=0x424
alt=32767 het=32767 rec=0 flg=2 opc=3
parent=06B52790 owner=00000000 nex=00000000 xsz=0x53c
EXTENT 0
addr=0717EE34
Chunk 717ee3c sz=
1332 freeable
"qkkele "
EXTENT 1
addr=0717F37C
Chunk 717f384 sz=
572 perm
"perm "
alo=388
Chunk 717f5c0 sz=
444 free
"
"
Chunk 717f77c sz=
36 freeable
"qkkkey "
EXTENT 2
addr=0717F7BC
Chunk 717f7c4
sz= 28
perm
"perm "
alo=28
Chunk 717f7e0 sz=
956 free
"
"
Chunk 717fb9c sz=
52 freeable "event string "
Total heap
size = 3420
FREE
LISTS:
Bucket 0 size=76
Bucket 1 size=268
Chunk 717f7e0 sz= 956
free
"
"
Chunk 717f5c0 sz=
444 free
"
"
Bucket 2 size=1036
Total free space
= 1400
UNPINNED RECREATABLE CHUNKS (lru
first):
PERMANENT CHUNKS:
Chunk 717f384
sz= 572
perm
"perm "
alo=388
Chunk 717f7c4 sz=
28 perm
"perm "
alo=28
Permanent space =
600
******************************************************
If
making these "full" heapdumps puts too much strain on your system, then it might
be easier to use event HEAPDUMP_ADDR which allows to dump heaps only with
specified descriptor address. There are other options as well, such is X$KSMHP
table to query any heap (which is, blah, highly unsupported) or
attaching directly to SGA shared memory segment and reading from
there.
Sorry for too long post, I'm currently too lazy to do
anything useful...
Tanel.
----- Original Message -----
From: Sultan Syed
To:
Multiple recipients of list ORACLE-L
Sent: Tuesday, January 06, 2004 3:49
PM
Subject: Top level heaps/subheaps
Hi,
I am getting little
confussion how the memory is allocated for
top-level heaps and subheaps in
shared pool.
How can we know what are all the top-level heaps and
subheaps and their hierarchy.
Is it possible to get it from any X$
tables.
Freeable chunks can be flushed out?If yes ,then why there should
be another type as recreatable chunks?
Please explain.
Thanks in
advance
Syed
--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: Tanel Poder
INET: tanel.poder.003_at_mail.ee
Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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Received on Tue Jan 06 2004 - 10:04:26 CST
